Acoustic recordings were used to investigate the cardiac responses of a captive dolphin (Tursiops truncatus) to sound playback stimuli. A suction-cup hydrophone placed on the ventral midline of the dolphin produced a continuous heartbeat signal while the dolphin was submerged. Heartbeats were timed by applying a matched-filter to the phonocardiogram. Significant heart rate accelerations were observed in response to playback stimuli involving conspecific vocalizations compared with baseline rates or tank noise playbacks. This method documents that objective psychophysiological measures can be obtained for physically unrestrained cetaceans. In addition, the results are the 1st to show cardiac responses to acoustic stimuli from a cetacean at depth. Preliminary evidence suggests that the cardiac response patterns of dolphins are consistent with the physiological defense and startle responses in terrestrial mammals and birds.
